This invention relates to a fuel injection nozzle, and particularly to a fuel injection nozzle whose nozzle hole area is variable.
As means for supplying fuel in an atomized state to an internal combustion engine such as a diesel engine, fuel injection nozzles are generally used. Such fuel injection A nozzles, as disclosed for example in Japanese Unexamined Patent Publication No. S.59-200063, have had a construction wherein a conical pressure-receiving surface is formed at the tip end of a needle valve axially slidably received inside a nozzle body and the needle valve is opened by a fuel pressure being made to act on this pressure-receiving surface and fuel is injected into a combustion chamber of the engine through a plurality of nozzle holes formed in the tip of the nozzle body.
However, with this construction, the fuel injection pressure, the injected amount and the injection speed are generally determined by a fuel injection pump, and also it is not possible to increase or decrease the total nozzle hole area. Consequently, during low-speed running of the engine the fuel injection pressure decreases and during low-load running the injection time becomes shorter and it is not possible to maintain a good combustion state, and it has been difficult to promote fuel combustion and achieve improvements in output and fuel consumption and reductions in combustion noise and NOx emissions.
As a measure to overcome this, in Japanese Unexamined Patent Publication No. H.6-241142 a fuel injection nozzle is proposed wherein a first set of nozzle holes (five) are provided on a circumference of a lower part of a wall of a needle valve having a closed tip and a second set of nozzle holes (five) of a different diameter from the first nozzle holes are provided on a different circumference and according to the load and speed of the engine either the first set of nozzle holes only are opened or both the first set of nozzle holes and the second set of nozzle holes are opened by the needle valve being moved axially in a sleeve.
In this related art, besides the problem that because the needle valve projects into the combustion chamber it undergoes thermal affects and distortion and the like are liable to occur, the injection angle with respect to the axis of the nozzle changes as a result of the sleeve fronting on the nozzle holes. Consequently, there has been a possibility of not being able to obtain optimum combustion with an existing combustion chamber shape designed with the injection angle assumed to be constant. Also, there has been the problem that to deal with this it becomes necessary to redesign the combustion chamber shape.
In Japanese Unexamined Patent Publication No. H.4-76266, a fuel injection nozzle is proposed wherein a well is formed in the tip part of a nozzle body, a plurality of nozzle holes (eight) connecting with the well are formed spaced in the circumferential direction in a wall enclosing the well, a rotating shaft is passed through a through hole formed axially down the center of the needle valve, a tip portion of this rotating shaft is positioned in the well, a plurality of grooves (four) which connect a fuel pressure chamber created inside the well when the needle valve opens to the nozzle holes are provided in the rotating shaft, and by rotation of this rotating shaft the number of open nozzle holes is switched between eight and four and the total area of the nozzle holes is thereby changed according to the load and speed of the engine.
This related art has the merit that because the rotating shaft turns about its axis to adjust the nozzle holes the injection angle with respect to the nozzle axis does not change substantially. However, with this related art, because the rotating shaft itself is used as a rotary valve, there have been problems in that when there is a machining error the whole shaft becomes a defective product and that it is liable to stop rotating smoothly due to bending or twisting.
Furthermore, the well wall forms a straight cylinder parallel with the nozzle axis, and the rotating shaft serving as the rotary valve is also cylindrical. Consequently, it has been difficult to fix the rotating shaft constituting the rotary valve during fuel injection, and even when the nozzle holes have been adjusted to a required degree of opening by the rotating shaft it has not been possible to avoid the rotating shaft slipping undesirably in its direction of rotation about its axis when a high fuel injection pressure acts at the nozzle holes and the relationship between the open holes and the grooves consequently slipping and the nozzle hole area becoming larger or smaller than the set size. For this reason, in the related art there has been the problem that it is not possible to accurately carry out control of the total nozzle hole area in accordance with the load and speed of the engine. Also, in the related art, because as described above there is no mechanism for fixing the rotary valve during fuel injection, there has been the problem that a large and relatively high-torque motor is needed to drive the rotating shaft and consequently the fuel injection nozzle becomes large.